The integrity of video surveillance systems can be compromised by cutting or otherwise disconnecting video and/or data cables between the monitoring system and the remote camera device. Loss of the control data signal is often detected immediately due to the common use of status polling algorithms that quickly identify lost communication links. Thus, the operator is alerted and the problem found before substantial risk is incurred. The loss of the video signal however, often goes unnoticed, particularly in medium to large systems, until there is a need to view the image from the remote camera.
In the past, the problem of compromised video signal integrity has been recognized and the solution has been to add circuits to the monitoring equipment at the receiving end of the system to detect the signal interruption. These systems detect the open circuit condition and report the status to the operator. The shortcoming of this method is that the monitoring equipment is often connected through other devices, i.e. multiplexers, quads, or VCRs, that have no video loss provision. The output of these devices can fool the video loss detection circuits by generating their own video signal, i.e. a blue screen, even if none is present at the input. In addition, none of the devices report an unterminated condition when the signal is present, but the connected device is set to high impedance. Furthermore, where means are provided for detecting improper load termination, these means are usually provided at the receiving end of a system where the video signals are transmitted from the camera or transmitting end to the control and monitoring console at the receiving end.
The requirement for both video and control data signals is common when installing Pan/Tilt/Zoom cameras, which require complex and expensive system wiring. Simplified installation has been addressed in a number of ways but the most desirable is to reduce the cabling to a single coaxial cable. Single coaxial cable systems are available that put video and control data on a single cable, but none detect an unterminated condition. Unterminated video is viewable on a video monitor, and appears brighter than normal, but the condition can be easily mistaken for misadjusted components, i.e. monitor, manual or auto-iris and amplifier gain. Again, this requires troubleshooting time to correct.
It is, therefore, an object of the present invention to provide a means to detect the presence of a proper termination load and thus proper connection on a coaxial cable.
It is a further object of this invention to provide means at the camera or transmitter end of the system to detect the presence of a proper termination load.
It is a further object of this invention to incorporate a control data detector/receiver to facilitate control functions on a single coaxial cable.